This chapter is from the book

This chapter is from the book

No one benefited more from the development of the computer than Santa Claus.
For centuries, humankind has put an immense burden on him to gather and process
information. Old St. Nick has to keep track of the following things:

Naughty children

Nice children

Gift requests

Homes with impassable chimneys

Women who want more from Santa than Mrs. Claus is willing to let him
give

Countries that shoot unidentified aircraft first and ask questions
later

Computers were a great boon at the North Pole. They are ideal for the
storage, categorization, and study of information.

The most basic way that information is stored in a computer program is by
putting it into a variable. However, this method is limited to relatively simple
usage. If Santa had to give each naughty child his or her own variable name,
he'd be working on the program for the next 12 holiday seasons at least, to
say nothing of the effect on his jolly disposition.

The list of naughty children is an example of a collection of similar
information. Each child's name is a string of text or some kind of Santa
Information System ID number. To keep track of a list of this kind, you can use
arrays.

Arrays are groups of related variables that share the same type. You
can have arrays of any type of information that can be stored as a variable.
Arrays can be used to keep track of more sophisticated types of information than
a single variable, but they are almost as easy to create and manipulate as
variables.

The following topics will be covered during this hour:

Creating an array

What a dimension of an array is

Giving a value to an array element

Changing the information in an array

Making multidimensional arrays

Sorting an array

Creating Arrays

Arrays are variables that are grouped together under a common name. The term
array should be familiar to you, though the meaning might not be so
clearthink of a salesman showing off his array of fabulous cleaning
products, or a game show with a dazzling array of prizes. Like variables, arrays
are created by stating the type of the variable being organized into the array
and the name of the array. The difference lies in the addition of the square
bracket marks [ and ].

You can create arrays for any type of information that can be stored as a
variable. For example, the following statement creates an array of string
variables:

String[] naughtyChild;

Here are two more examples:

int[] reindeerWeight;
boolean[] hostileAirTravelNations;

NOTE

Java is flexible about where the square brackets are placed when an array is
being created. You can put them after the variable name, instead of after the
variable type, as in the following:

String niceChild[];

To make arrays easier for humans to spot in your programs, you should
probably stick to one style rather than switching back and forth, though Java
allows both styles of usage.

The previous examples create arrays, but they do not store any values in them
initially. To do this, you must either use the new statement along with
the variable type or store values in the array within { and }
marks. You also must specify how many different items will be stored in the
array. Each item in an array is called an element. The following
statement creates an array and sets aside space for the values that it will
hold:

int[] elfSeniority = new int[250];

This example creates an array of integers called elfSeniority. The
array has 250 elements in it that can be used to store the months that each of
Santa's elves has been employed at the Pole. If the rumors are true and
Santa runs a union shop, this information is extremely important to keep track
of.

When you create an array with the new statement, you must specify
the number of elements. Each element of the array is given an initial value when
it is set up with new; the value depends on the type of the array. All
numeric arrays have the value 0, char arrays have the value
'\0', and boolean arrays have the value
false. A String array and all other objects are created with
the initial value of null.

For arrays that are not extremely large, you can set up their initial values
at the same time that you create them. The following example creates an array of
strings and gives them initial values:

The information that should be put into elements of the array is placed
between { and } brackets, with commas separating each element.
The number of elements in the array is not specified in the statement because it
is set to the number of elements in the comma-separated list. Each element of
the array in the list must be of the same type. The preceding example uses a
string for each of the reindeer names.

Once the array is created, you cannot make more space and add another
variable to the array. Even if you recall the most famous reindeer of all, you
couldn't add "Rudolph" as the ninth element of the
reindeerNames array. A Java compiler won't let poor Rudolph join
in any reindeerNames.